Implantable medical device and lithium battery

ABSTRACT

A lithium battery includes a housing and a first electrode and a second electrode provided within the housing. A first tab is coupled to the first electrode and a second tab coupled to the second electrode. A pin is coupled to the second tab and extends to a location outside the housing. At least one of the first tab, the second tab, and the pin are formed from a material comprising vanadium.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(e) ofU.S. Provisional Patent Application No. 60/785,881 filed on Mar. 24,2006 and U.S. Provisional Patent Application No. 60/827,621 filed Sep.29, 2006, the entire disclosures of which are incorporated herein byreference.

BACKGROUND

The present inventions relate generally to the field of implantablemedical devices (IMDs). More particularly, the present inventions relateto IMDs such as implantable neurological stimulation (INS) devices thatinclude features intended to reduce magnetic resonance imaging (MRI)distortion.

Implantable neurological stimulation devices (sometimes referred to asan implantable neuro stimulator or INS) generate electrical stimulationsignals that are used to influence the human nervous system or organs.Conventionally, the INS has been surgically implanted into a patient ina subcutaneous pocket in the abdomen, pectoral region, or upper buttocksarea. Electrical contacts carried on the distal end of a lead are placedat the desired stimulation site (e.g., at a location in the spine ordirectly in the brain) and the proximal end of the lead is connected tothe INS.

It may be desirable to implant the INS at a location in the patient'shead in cases where the distal end of the lead is provided at a sitedirectly in the brain. For example, it may be desirable to implant theINS under the scalp of the patient's head (either on top of the surfaceof the skull or in a pocket or cutout formed in the skull).

One difficulty with implanting medical devices such as INS deviceswithin the body of a patient is that the materials used in such devicesmay tend to alter or distort images produced during MRI scans. Suchdistortion may extend beyond the immediate surrounding area of thedevice.

Accordingly, there is a need to provide an implantable medical devicesuch as an INS that exhibits reduced image distortion when MRI scans aretaken as compared to conventional devices. There is also a need toprovide an improved implantable medical device that utilizes differentmaterials for components to minimize MRI image distortion. There isfurther a need to provide an improved method of performing an MRI scanthat provides less image distortion as compared to conventional scanningmethods.

SUMMARY

An exemplary embodiment relates to a lithium battery that includes ahousing, a first electrode provided within the housing, a first tabcoupled to the first electrode, a second electrode provided within thehousing, and a second tab coupled to the second electrode. A pin iscoupled to the second tab that extends to a location outside thehousing. At least one of the first tab, the second tab, and the pin areformed from a material comprising vanadium.

Another exemplary embodiment relates to a lithium battery that includesa housing, a first current collector electrically coupled to a positiveelectrode, and a second current collector electrically coupled to anegative electrode. A terminal is coupled to one of the first currentcollector and the second current collector. At least one of the firstcurrent collector, the second current collector, and the terminalcomprise a material selected from the group consisting of vanadium andvanadium alloys.

Another exemplary embodiment relates to an implantable medical devicethat includes a housing configured for implantation in a human body. Alithium battery is provided within the housing that includes a memberformed of a vanadium material, the member selected from the groupconsisting of a terminal and a tab for an electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) through 1(f) illustrate MRI image distortion caused by theuse of a titanium material.

FIGS. 2( a) through 2(f) illustrate MRI image distortion caused by theuse of a ferrite material.

FIGS. 3( a) through 3(f) illustrate MRI image distortion caused by theuse of a steel material.

FIG. 4 is a cutaway perspective view of an implantable medical device inthe form of an INS according to an exemplary embodiment.

FIG. 5 is a partial cutaway perspective view of a battery configured foruse in an INS shown such as that shown in FIG. 4 according to anexemplary embodiment.

FIG. 6 is an exploded perspective view of the battery shown in FIG. 5according to an exemplary embodiment.

FIG. 7 is a schematic plan view of a hybrid or circuit board in whichcomponents that may cause MRI image distortion are not provided adjacentone another.

FIG. 8 is a schematic cross-sectional view of an implantable medicaldevice according to an exemplary embodiment in which a potting materialor adhesive includes a shimming material provided therein.

FIG. 9 is a schematic cross-sectional view of an implantable medicaldevice according to an exemplary embodiment illustrating a shimmingmaterial provided as a plating provided on the inner surface of thedevice housing.

FIG. 10 is a schematic cross-sectional view of an implantable medicaldevice according to an exemplary embodiment illustrating a shimmingmaterial provided as a plating provided on the outer surface of thedevice housing.

FIG. 11 is a schematic cross-sectional view of an implantable medicaldevice according to an exemplary embodiment illustrating a shimmingmaterial provided on a portion of the device housing or casing.

FIG. 12 is a schematic cross-sectional view of an implantable medicaldevice according to an exemplary embodiment illustrating a shimmingmaterials having differing thicknesses provided on the device housing.

FIG. 13 is a schematic sectional plan view of an implantable medicaldevice according to an exemplary embodiment.

FIG. 14 is a schematic cross-sectional view of the device shown in FIG.13 illustrating a shimming material coated or plated on the devicehousing in locations other than those in which recharge or telemetrycoils are provided.

FIG. 15 is a drawing illustrating several possible coating or platingpatterns that may be used to provide a shimming material on animplantable medical device.

FIG. 16 is a schematic cross-sectional view of an implantable medicaldevice according to an exemplary embodiment having shimming componentscoupled to the device housing.

FIG. 17 is a schematic plan view of an implantable medical device havingshimming components provided on the exterior surface of the deviceaccording to an exemplary embodiment.

FIG. 18 is a schematic cross-sectional view of an implantable medicaldevice according to another exemplary embodiment.

FIG. 19 is a schematic plan view of an implantable medical deviceaccording to an exemplary embodiment having shimming components providedin a header block.

FIG. 20 is an MRI image of a battery housing or casing made of stainlesssteel.

FIG. 21 is an MRI image of a battery housing or casing made of analuminum housing.

DETAILED DESCRIPTION

According to an exemplary embodiment, an implantable medical device(e.g., an INS) is provided that includes features intended to reduce theamount of MRI image distortion. According to one exemplary embodiment,one or more components of the device may utilize materials or coatingshaving predefined magnetic permeabilities that are intended to reduce oroffset image distortion. According to another exemplary embodiment, oneor more components of the device may be configured to reduce theoccurrence of eddy currents generated during an MRI scan (e.g., byreducing or varying the thickness of various components).

The human body is composed mostly of water, which has a relativepermeability of 0.9999912. Accordingly, water is slightly diamagnetic(see, e.g., Table 1).

TABLE 1 Classification of Materials Classification DiamagneticParamagnetic Ferromagnetic Permeability <1 >1 >>1

When the human body undergoes an MRI scan, materials having magneticpermeabilities that differ greatly from that of water when the magneticfield is applied will cause distortion in the resulting MRI image. Ithas been observed that the larger the difference between the magneticpermeability of the material and the magnetic permeability of water atthe relatively high magnetic field strengths generated during an MRIscan, the greater the image distortion will be.

For example, FIGS. 1( a) and 1(b) illustrate an image taken during anMRI scan (at a magnetic field strength of 1.5 Tesla) of a 20 cm by 40 cmphantom cylinder filled with water to simulate a human head without animplanted. INS. FIGS. 1( c) and 1(d) are images taken using a spin echoMRI scan of the phantom cylinder with a titanium can taped to one sideof the cylinder. Areas 5 of image distortion are visible in the imagesas relatively dark portions. Such distortion is increased when using agradient echo MRI scan, as shown in FIGS. 1( e) and 1(f).

TABLE 2 Relative magnetic permeabilities of selected materials MaterialRelative Permeability Water 0.9999912 Copper 0.9999906 Silver 0.9999736Lead 0.9999831 Air 1.00000037 Oxygen 1.000002 Aluminum 1.000021 Titanium6-4 (Grade 5) 1.00005 Palladium 1.0008 Platinum 1.0003 Manganese 1.001Cobalt 250 Nickel 600 Iron 280,000

Table 2 lists relative magnetic permeabilities for various materials atrelatively low magnetic field strengths (data obtained from variouspublicly available sources such as http://www.matweb.com). As seen inTable 2, while titanium has a relative permeability of 1.00005, iron (amajor component of steel) has a relative permeability of 280,000. Assuch, it would be expected that including iron in an INS would result inrelatively significant image distortion. In general, materials that areferromagnetic at room temperature—iron, cobalt, and nickel—have relativepermeabilities that greatly exceed that of water at relatively highmagnetic field strengths, and thus would be expected to distort MRIimages far more than materials that have magnetic permeabilities closerto that of water.

FIGS. 2-3 provide further illustrations of this principle. In contrastto the relatively minor distortion shown in FIGS. 1( c) through 1(f)where a titanium can was coupled to the phantom cylinder, FIGS. 2 and 3illustrate MRI image distortion resulting from the use of a ferritematerial (FIG. 2) and a steel material (FIG. 3) in place of the titaniumcan (FIGS. 2( a), 2(b), 3(a), and 3(b) are control images similar tothose shown in FIGS. 1( a) and 1(b)). As shown in FIGS. 2 and 3, forferrite and steel materials, the resultant image distortion is fargreater than was present using the titanium material.

While the data in Table 2 illustrates relative magnetic permeabilitiesof various materials, the inventors have observed that certain materialsmay exhibit different characteristics at the relatively high fieldstrengths used in MRI scans. For example, while Table 2 suggests thatcopper is slightly diamagnetic at low field strengths, it has beenobserved that the permeability of copper tends to shift toward beingrelatively paramagnetic at higher field strengths. In selectingmaterials as described below (e.g., for use in shimming implantablemedical devices), the high-field-strength permeabilities of thematerials should be assessed to confirm that such materials will providethe desired effect when subjected to the relatively high magnetic fieldstrengths used in MRI scans.

According to an exemplary embodiment, an implantable medical device maybe designed such that it produces less MRI image distortion than wouldbe exhibited by a conventional device. Various different design criteriamay be employed in order to accomplish this goal. For example, accordingto one exemplary embodiment, the amount of ferromagnetic materials(e.g., nickel, cobalt, iron, and ferrites) used in the device may bereduced. While all metals would be expected to produce some degree ofMRI image distortion, reducing the amount of ferromagnetic materialswould have a greater effect on image distortion than reducing the amountof slightly diamagnetic and paramagnetic materials.

It may also be desirable to minimize the eddy currents that may beinduced during imaging. Eddy currents cause distortion, although suchdistortion is not expected to be as significant as that caused byferromagnetic materials. Reducing the eddy currents associated with aparticular device may be accomplished principally by reducing or varyingthe thickness of various components as compared to conventionalcomponents.

It may also be desirable to remove or shim non-ferromagnetic materialsthat have permeabilities that differ from that of water. For example,relatively large components that are made of paramagnetic materials maybe shimmed with a diamagnetic material to balance out the paramagneticmaterial and to reduce image distortion. According to an exemplaryembodiment, materials that have permeabilities that differ from water athigh field strengths (e.g., 1.5 or 3 Tesla) such as those found in MRIimaging applications may be shimmed, removed from the device, or made ofmaterials less likely to cause significant image distortion.

FIG. 4 illustrates an implantable medical device 100 in the form of animplantable neurological stimulation (INS) device according to anexemplary embodiment. As shown in FIG. 4, the device 100 includes abattery 10, coils 120 (e.g., for recharging the battery or fortelemetry), a wiring board or hybrid 130 (e.g., a circuit board havingvarious electronic components soldered or otherwise provided thereon), adevice enclosure 140 (e.g., a housing or casing), interconnects 150, anda connector or header 160 (the connector includes an aperture as shownat the right side of FIG. 4 that is configured to have a lead insertedtherein).

FIGS. 5-6 provide further illustrations of the components of the battery10 that may be used in conjunction with device 100. It should be notedthat the battery 10 may be a non-rechargeable (i.e., primary) or arechargeable (i.e., secondary) lithium-based battery according tovarious exemplary embodiments.

With reference to FIG. 5, the battery 10 includes a battery case orhousing 20 provided in the form of a relatively thin-walled hollowstructure that is configured for having a plurality of componentsprovided therein. A liner 24 is provided adjacent or proximate thehousing 20 to separate internal components of the battery 10 from thehousing 20. A cover or cap 22 is provided at a top surface of thebattery 10 and may be coupled (e.g., welded, adhered, etc.) to thehousing 20. A headspace insulator 26 is provided within the housing 20to provide a space in which connections may be made to electrodesprovided within the housing 20 (additionally, a coil liner 27 as shownin FIG. 6 may be provided which may act to separate a cell element fromthe headspace region of the battery 10). A member or element 29 in theform of a bracket may be provided to couple a current collector of anegative electrode to the case and/or to the housing.

The battery 10 includes a cell element 30 provided within the housing 20that comprises at least one positive electrode and at least one negativeelectrode. Each of the electrodes has a member or element in the form ofa tab or current collector coupled thereto. As illustrated in FIGS. 5-6,electrode 32 is a positive electrode having tab 34 coupled thereto, andelectrode 36 is a negative electrode having a tab 38 coupled thereto. Insuch a configuration, the battery 10 has a case negative design.According to other exemplary embodiments in which the battery includes acase positive or neutral design, the electrodes may be reversed (e.g.,electrode 32 would be the negative electrode and electrode 36 would bethe positive electrode).

The current collector 34 of the positive electrode is electricallycoupled to a pin or terminal 25 (e.g., a feedthrough pin) that isprovided such that it protrudes through an opening or aperture 23provided in the cover 22. In such an embodiment, the pin would act asthe positive terminal for the battery and may be connected at a distalend to a feature included in a hybrid (either directly or indirectly).In a case neutral or case positive battery design, the pin 25 may becoupled to a tab provided on a negative electrode.

A separator 40 is provided intermediate or between the electrodes, andan electrolyte 50 is also provided in the housing 20 (e.g., through anopening or aperture 28 in the form of a fill port provided in the cover22 of the battery 10).

In conventional lithium batteries used in implantable medical deviceapplications, the housing of the battery is made from a metal such asstainless steel. To reduce the image distortion caused by the battery10, the housing 20 may be made of a material that is less likely toresult in substantial MRI image distortion such as one or more of thefollowing materials: (1) aluminum or an aluminum alloy (including the3000 series); (2) aluminum foil/polymer composites with heat-sealableedges (i.e., a “foil pack”); (3) titanium and titanium alloys (alloysinclude Grade 5, Grade 9, Grade 1, and SP700 (Ti-4.5A1-3V-2Mo-2Fe)); and(4) copper and copper alloys.

It should be noted that for reasons of electrochemical stability, somecase materials should only be used at one or the other of the batterypolarities, or at a neutral potential. For example, for manylithium-based battery configurations, aluminum may be an inappropriatehousing material if the housing 20 is at the negative polarity of thecell, and stainless steel or titanium would be inappropriate at thepositive cell polarity. This housing material choice depends on batterychemistry and knowledge of material stability. FIGS. 20 and 21illustrate MRI images taken of a stainless steel battery case (FIG. 20)and an aluminum battery case (FIG. 21). As shown, the amount ofdistortion caused by the aluminum battery case is significantly lessthan that caused by the stainless steel battery case.

Other components of the battery 10 may also be formed of materials thatare less likely to cause significant MRI image distortion. For example,according to an exemplary embodiment, components such as the pin 25(which is conventionally made of a titanium alloy or niobium), the tabs34, 38, and the bracket 29 may be made of aluminum, copper, vanadium, oralloys and combinations thereof, and the header and fill port 28 may bemade one or more of the materials described above with respect to thehousing 20.

According to an exemplary embodiment in which a battery has a casenegative design, the tab coupled to the negative electrode (e.g., tab 38as shown in FIG. 6) may be formed of vanadium or a vanadium alloy.According to another exemplary embodiment in which the a battery has acase neutral or case positive design, the pin 25 and/or the tab coupledto the negative electrode (which would be tab 34 as shown in FIG. 6,since the electrodes would be reversed in such a configuration) may beformed from vanadium or a vanadium alloy. According to another exemplaryembodiment, the tab coupled to the positive electrode may be formed fromvanadium or a vanadium alloy where the potential of the positiveelectrode does not exceed approximately 3.6 volts (i.e., does not exceedthe corrosion potential of vanadium). Other features of the battery 10may also be formed of vanadium or a vanadium alloy according to otherexemplary embodiments, such as the housing 20 or the cover 22.

One advantageous feature of using vanadium is that in addition to beingbeneficial for reducing MRI image distortion, vanadium may also bewelded to both copper and titanium (e.g., which would allow acase-negative design with a titanium case such that vanadium could bewelded from a copper electrode to the titanium case). In otherapplications, a case-positive design may be used in which an aluminuminterconnect from an aluminum positive electrode could be welded to analuminum case.

The conductors that connect the pin 25 to the hybrid 130 may be made ofaluminum, copper, titanium, vanadium, or alloys thereof. Alternatively,the pin 25 may be connected directly to the hybrid 130 without the needfor separate connectors. In another example, non-ferrous conductors suchas titanium or titanium alloys may be used to connect the pin 25 to thebal-seals.

According to an exemplary embodiment in which the pin 25 is provided fora hermetically sealed battery, the pin may be made of a titanium alloy(e.g., Grade 5, Grade 9, or SP700). According to another exemplaryembodiment, the pin could also include aluminum.

According to an exemplary embodiment in which the pin 25 is provided fora non-hermetically sealed battery, it may include a crimped or “rivetfeedthrough” with a polymer grommet. The rivet portion would be the samematerial as listed above for hermetically sealed batteries. The polymermay be a polyolefin (e.g., a low-creep material such as polypropylene orHDPE) or may be ETFE.

According to an exemplary embodiment, the negative active material maybe selected from graphite, Li₄Ti₅O₁₂, lithium alloying elements such asaluminum, tin, and silicon, and combinations thereof, and the positiveactive material may be selected from LiCoO₂; LiM_(x) Ni_(1-x)O₂ (where Mis a metal such as Ti or Al); LiMn₂O₄; LiCo_(x)Mn_(y)Ni_(z)O₂ (wherex+y+z=1), and combinations thereof.

Various components of the implantable medical device 100 may also bemade from materials that are less likely to produce significant MRIimage distortion. For example, screws and set screw blocksconventionally used in assembling the device 100 are formed of stainlesssteel, which has a significant ferrous content. According to anexemplary embodiment, the device 100 utilizes connectors that are formedfrom a material (e.g., titanium or a titanium alloy, a polymericmaterial such as polysulfone or polyether ether ketone, etc.) that isboth biocompatible and has a reduced tendency to distort MRI images.

Implantable medical devices such as that shown in FIG. 4 may alsoutilize one or more electrical contacts (not shown) within the device.Presently, such contacts are provided in the form of platinum springcontacts (referred to as Bal-seals) inside of housings made from analloy including chromium, cobalt, molybdenum, and nickel. According toan exemplary embodiment, the device 100 utilizes a low permeabilitystainless steel (e.g., having a permeability of between approximately1.008 and 1.02) in place of the alloy formerly used to produce thehousing. According to another exemplary embodiment, the housing may bemade of platinum or a platinum alloy. According to yet another exemplaryembodiment, the housing may be made of a creep resistant polymer (e.g.,polysulfone or thermoplastic polyether ether ketone (referred to asPEEK)). One advantageous feature of utilizing a polymer is that doing sowould not only reduce the image distortion due to the use of ferrousmaterials, but it would also eliminate the image distortion caused byeddy currents. According to still yet another exemplary embodiment, thehousing may be made of a platinum-clad titanium material.

The wiring board or hybrid 130 includes various features such aselectronic chips and the like. Conventionally, such components mayutilize ferrite materials (e.g., as cores for coils or inductors).According to an exemplary embodiment, the hybrid 130 is produced withoutthe use of ferrite materials (e.g., telemetry and/or recharge antennasmay utilize air core antennas).

Conventional bonding pads utilized with the hybrid 130 may be formed ofnickel 200 or Kovar (an alloy of iron, nickel, and molybdenum).According to an exemplary embodiment, the bonding pads utilized with thehybrid may be formed of titanium, platinum, copper, or alloys thereof.

The coils 120 utilized with the device 100 have conventionally beenformed of copper, and have included ferrite cores. Because copper has apermeability close to that of water, and acts as an excellent conductor,it may be desirable to continue to use copper for the coils 120.According to an exemplary embodiment, copper coils with air cores areused in place of the copper coils with ferrite cores used inconventional designs. According to other exemplary embodiments, a memberor element such as a ring of shimming material (e.g., platinum,aluminum) may be provided adjacent the coil or at a location proximatethe coil.

The device enclosure 140 has conventionally been made of grade 1titanium, which has a permeability that is relatively close to that ofwater. However, because the device enclosure 140 has a relatively largesurface area, relatively significant eddy currents can be created on itduring an MRI scan, which may result in image distortion. In order toreduce the eddy currents formed during an MRI scan, the device enclosuremay be formed of a titanium having a higher resistivity. For example,according to an exemplary embodiment, the device enclosure may utilize agrade 9 titanium (or another grade or alloy of titanium having a higherresistivity).

According to other exemplary embodiments, different materials may beused to form the device enclosure 140. For example, according to anexemplary embodiment, the enclosure is constructed out of a polymer andthen covered using a diamond-like coating for hermeticity. It isexpected that such a construction would significantly reduce the eddycurrents created on the enclosure during a scan and the resulting imagedistortion. According to another exemplary embodiment, the deviceenclosure 140 may be constructed using a creep resistant polymer such asthermoplastic polyether ether ketone or polysulfone, which wouldcompletely eliminate the eddy currents created on the enclosure during ascan.

According to other exemplary embodiments, the device enclosure 140 maybe formed such that is includes a variety of thicknesses to createreflections that reduce the loop area of the eddy currents during ascan. For example, the enclosure 140 may be made with areas (e.g.,zones, regions, etc.) that are thinner than surrounding areas to furtherincrease the electrical resistivity to minimize eddy currents. Accordingto one exemplary embodiment, the enclosure 140 may be produced in ametal injection molding process (e.g., in which a titanium housing isinjection molded) such that a plurality of areas or regions of thehousing are formed as having different thicknesses. According to anotherexemplary embodiment, the housing may have a substantially uniformthickness and have components coupled (e.g., welded) thereto to increasethe thickness of particular regions of the housing (e.g., a titaniumhousing may have titanium, platinum, or aluminum strips of materialwelded thereto).

Extensions, tethers, or other accessories may be constructed usingmaterials that do not cause significant image distortion. For example,according to an exemplary embodiment, extensions or tethers may beconstructed using platinum irridium filers and contacts.

According to an exemplary embodiment, all or a portion of an implantablemedical device such as an INS may be shimmed using materials havingknown magnetic permeabilities in order to decrease image distortion whenan organism in which the device 100 is implanted undergoes an MRI scan.For example, if a device has a relative magnetic permeability that makesit paramagnetic overall, it may be advantageous to provide a diamagneticshimming material in order to “balance” the paramagnetic character ofthe device, thus bringing the overall magnetic permeability of thedevice closer to that of water. Shimming may be accomplished in anynumber of ways, including coating or plating (e.g., cladding) the deviceor portions thereof with a shimming material (e.g., a titanium housingmay be shimmed with platinum or palladium). Another manner in whichshimming may be accomplished is by providing components within thedevice that have desired shimming properties. These and other methods ofshimming a medical device will be described hereafter with reference tothe accompanying drawings. Materials used to shim the device may beselected based on a variety of considerations including their magneticpermeability characteristics and biocompatibility, and may include, forexample, titanium, palladium, platinum, silver, copper, manganese,aluminum, and alloys and combinations thereof.

While the goal of shimming the implantable medical device with ashimming material is to produce a device that has a magneticpermeability as close to water as possible (and thus, as close aspossible to that of the organism into which it will be implanted), insome circumstances it may be adequate to simply add some shimmingmaterial such that there is less MRI image distortion than if noshimming material were added. The degree of acceptable MRI imagedistortion that is acceptable or suitable in a given circumstance mayvary depending on the location of the device implantation and otherfactors, and the amount of shimming material added to the device shouldbe selected such that it is adequate to provide a suitably small amountof image distortion under the circumstances.

According to an exemplary embodiment, a method of determining theappropriate amount of shimming material to be added to an implantablemedical device includes creating a prototype of the device and creatingan electromagnetic model of the device prototype. The prototype may thenbe analyzed to determine the aggregate relative magnetic permeability ofthe device prototype (e.g., by viewing the field perturbation in amagnetic field). Based on the aggregate relative magnetic permeabilityof the device prototype, it may be determined whether the shimmingmaterial should be paramagnetic or diamagnetic. The appropriate shimmingmaterial may then be selected and added to the device prototype. Afterthe shimming material is added to the device prototype, the device maybe re-modeled to determine its new aggregate relative magneticpermeability. Shimming material may again be added and the devicere-modeled in an iterative manner until the desired level of aggregatemagnetic permeability is reached.

To determine the proper placement of the shimming material, it isdesirable to first understand which components of the device are mostlikely responsible for the image distortion (i.e., the “problemcomponents”). To enhance the ability of the shimming material to performits desired function, it may be beneficial to design the device suchthat the problem components are not grouped together, but rather arespread apart. FIG. 7 illustrates a circuit board or hybrid 200 thatincludes two problem components 202 and 204. As illustrated, the problemcomponents 202 and 204 are not provided proximate or adjacent oneanother, but rather are spread out such that they are on opposite endsof the hybrid 200 to reduce the amount of localized image distortioncaused by the components. The particular placement and location of theproblem components may vary according to various exemplary embodiments.

According to another exemplary embodiment, problem components may beprovided proximate or adjacent to other components that have oppositemagnetic permeabilities (e.g., a paramagnetic component may be providednext to one or more diamagnetic components) in order to provide somedegree of localized cancellation of the undesirable effect caused by thecomponents (e.g., to effectively “shim” the problem components). Forexample, as shown in FIG. 7, if component 204 is diamagnetic, components206 and 208 may be paramagnetic.

According to other exemplary embodiments, shimming materials may beincorporated within other materials used within an implantable medicaldevice. For example, as shown in FIG. 8, an implantable medical device300 includes a housing or casing 302 in which a hybrid or circuit board310 is provided. A potting or filler material 320 may be provided withinthe device 300, with a shimming material provided or loaded in thepotting material 320. According to an exemplary embodiment, the pottingmaterial is made of epoxy or silicon rubber and has a suitable shimmingmaterial provided therein (e.g., if the device is paramagnetic overall,a diamagnetic material such as silver may be incorporated in the pottingmaterial).

Similar to the embodiment shown in FIG. 8, an epoxy or other adhesiveused to secure various components within the device 300 may include ashimming material provided or loaded therein. One advantageous featureof providing shimming material in a potting material or in an adhesiveprovided within the housing 302 of the device 300 is that there islittle or no impact on the size of the device, since the shimmingmaterials would be provided in spaces that are either unoccupied or inmaterials that are already used in the device.

Other components of the device may also be loaded with a shimmingmaterial. For example, as shown in FIG. 4, an insulator cup 170 isprovided in the device 100 for housing certain components of the device100. According to an exemplary embodiment, the insulator cup 170 may beloaded with a shimming material in order to improve the permeability ofthe device 100.

According to other exemplary embodiments, all or a portion of the deviceenclosure may be coated, plated, or clad with a shimming material. FIGS.9 and 10 illustrate a shimming material coated (e.g., plated, clad,etc.) on a housing of an implantable medical device according to twoexemplary embodiments. FIG. 9 illustrates a device 400 having a housingor casing 402 with a shimming material 410 provided on an outer orexterior surface of the housing 402. FIG. 10 illustrates a device 500having a housing or casing 502 with a plating or coating 510 provided onan inner or interior surface of the housing 502. According to anexemplary embodiment, the housings shown in FIGS. 9 and 10 are made froma paramagnetic material, and the shimming material is made from adiamagnetic material. According to other exemplary embodiments, thehousings may be made of paramagnetic materials and the shimming materialmay be a diamagnetic material.

It should be noted that where the shimming material is provided on anexterior surface of the device housing, it is advisable to ensure thatthe material selected for the plating or coating material bebiocompatible with the organism into which the device is to beimplanted. The thickness of the shimming material may vary according tovarious exemplary embodiments. According to an exemplary embodiment, theshimming material has a thickness of between approximately 0.005 inches(0.125 mm) and 0.040 inches (1 mm).

While FIGS. 9 and 10 illustrate a shimming material provided on eitherthe exterior or interior surface of the housing, it should be noted thatshimming material may be provided on both the exterior and interiorsurfaces (and further, that only a portion of the exterior and/orinterior surfaces may have shimming materials provided thereon). Theshimming materials provided on the exterior surface and the interiorsurface may have identical or different compositions. Further, more thanone type of shimming material may be provided on the exterior and/orinterior surfaces of the housing (e.g., silver may be provided on aportion of the exterior surface and titanium on another portion, etc.).

According to a particular exemplary embodiment, the interior and/orexterior of a housing for an implantable medical device is at leastpartially coated (e.g., clad, plated, etc.) with titanium or a titaniumalloy to a thickness sufficient to reduce or minimize image distortioncaused by the device enclosure. According to another particularexemplary embodiment, the interior and/or exterior of a housing for animplantable medical device is at least partially coated (e.g., clad,plated, etc.) with silver or a silver alloy to a thickness sufficient toreduce or minimize image distortion caused by the device enclosure(e.g., up to approximately 0.005 inches).

While FIGS. 9 and 10 illustrate embodiments in which the entire interiorand/or exterior surfaces of the device housings are coated or platedwith a shimming material, it should be noted that according to otherexemplary embodiments, the shimming or plating material may be providedon only a portion of the housing or casing. As shown in FIG. 11, animplantable medical device 600 includes a battery 610 and a hybrid orcircuit board 620 provided within a housing or casing 602. The hybrid620 includes two components 622 and 624 that are most responsible forproducing image distortion in an MRI image (i.e., they are so-called“problem components”). Shimming materials are providing on housing 602only in locations proximate or adjacent to the problem components 622,624 (shown as regions or areas of shimming materials 630 and 632). Inthis manner, the shimming material is placed in the location where itmay be most efficacious in reducing the amount of MRI image distortioncaused by the problem components. One advantage of such a configurationis that the amount of shimming material required to provide adequateshimming of the device may be more closely tailored to the amountactually needed, which may result in less shimming material being usedthan if the entire interior and/or exterior surface of the housing werecoated with the shimming material. The provision of separate regions ofcoating or plating on the device housing may accomplished using maskingtechniques or any other suitable technique.

The thickness of the shimming material may vary according to variousconsiderations, including the particular amount of shimming needed at aparticular location within the housing. FIG. 12 illustrates animplantable medical device having a housing 702 with a battery 710 and ahybrid or circuit board 720 provided therein. In the embodiment shown,the battery 710 has been determined to be less responsible for MRI imagedistortion than the hybrid 720. Accordingly, a greater amount ofshimming material is provided proximate or adjacent the hybrid 720 ascompared to that provided adjacent the battery 710. This is illustratedby a first plated or coated shimming material 740 having a firstthickness provided adjacent the battery 710 and a second plated orcoated shimming material 750 provided adjacent the hybrid 720. Accordingto an exemplary embodiment, the two shimming materials 740 and 750 havethe same composition. According to other exemplary embodiments, theshimming materials 740 and 750 have different compositions (e.g.,shimming material 740 may comprise platinum, while shimming material 750may comprise aluminum). The composition of the shimming materials andthe coating/plating thicknesses selected will vary according to variousexemplary embodiments in accordance with the necessary amount ofshimming in particular regions within the housing.

In certain cases, providing a shimming material in the form of a coatingor plating on the device housing may adversely affect charging ortelemetry of the device. In such cases, it may be desirable to providethe coatings in a manner that will not affect such functions. Forexample, FIGS. 13-14 illustrate schematic views of an implantablemedical device 800 according to an exemplary embodiment. Device 800includes a housing or casing 802 having a battery 810 and a hybrid orcircuit board 820 provided therein. A recharging or telemetry coil 812is provided proximate the battery 810. To reduce or eliminate theadverse effect that may be caused by coating of the housing 802, coatingis not provided in the areas of the housing proximate the recharging ortelemetry coil 812. As shown in FIG. 14, coatings 830 and 832 areprovided adjacent the battery and coatings 834 and 836 are providedadjacent the hybrid 820. Spaces are provided between coatings 830 and834 and between coatings 832 and 836 in the regions 840, 842, and nocoating is provided in regions 844 and 846. In this manner, no coatingis provided in regions 840, 842, 844, and 846 proximate therecharging/telemetry coil. The selective coating of the housing may beaccomplished by masking or other suitable methods.

The plating or coating of the device housings as shown in FIGS. 9-14 maybe accomplished by any suitable method (e.g., PVD, CVD, sintering,etc.). According to an exemplary embodiment, a paramagnetic material iscoated on the device housings by physical vapor deposition. It shouldalso be noted that while FIGS. 11-14 illustrate plating on the innersurface of the device housings, similar results may be obtained bycoating or plating the exterior surface of such devices (e.g., thecoating shown within the housings in FIGS. 11-14 may instead be providedon an exterior surface of the housing).

It should be noted that features shown in FIGS. 8-14 may be combined asmay be desired. For example, the embodiment shown in FIG. 14 may bemodified to include coatings having different thicknesses (as shown,e.g., in FIG. 12) and/or to have coatings provided adjacent problemareas (as shown, e.g., in FIG. 11 with respect to problem areas-adjacentthe hybrid). A potting material loaded with a shimming material may alsobe used. Various combinations of such features are possible, and allsuch combinations are intended to fall within the scope of the presentdisclosure.

Any of a variety of coating methods may be used to provide shimmingmaterial on all or a portion of a component such as the housing. Forexample, all or a portion of the housing may be completely coated with ashimming material. According to other exemplary embodiments, the coatingmay be applied as having any of a variety of patterns using masking orother techniques that are now known or may be hereafter developed. FIG.15 illustrates four coating patterns (formed, e.g., using maskingtechniques or other suitable techniques) that may be applied to all or aportion of a component according to various exemplary embodiments,although it should be understood that numerous other patterns may bepossible. Additionally more than one different type of pattern may beapplied to the same component.

As an alternative to (or in addition to) plating or coating the housingwith a shimming material, pieces (e.g., members, elements, etc.) ofshimming material may be coupled to the housing by welding, soldering,adhesive, or by any other suitable method. FIG. 16 illustrates aschematic cross-sectional view of an implantable medical device 900having a housing 902 having a hybrid or circuit board 910 providedtherein. Two pieces of shimming material 920 and 922 are coupled to aninterior surface of the housing 902 in areas unoccupied by components ofthe device 900. Any number of shimming components may be coupled to thehousing having any of a variety of sizes, shapes, and/or configurationsaccording to various exemplary embodiments.

FIG. 17 illustrates a schematic plan view of an implantable medicaldevice 1000 according to another exemplary embodiment. The device 1000includes a hermetically sealed housing or casing 1002 that has rails1010 and 1020 welded to the exterior surface thereof. The rails 1010 and1020 are made of titanium according to an exemplary embodiment and havea shimming material loaded into the rails. According to an exemplaryembodiment, the rails have a thickness of between approximately 1 mm and4 mm, although the size, shape, and/or configuration of the rails mayvary according to other exemplary embodiments. According to otherexemplary embodiments, the rails may be coupled to an interior surfaceof the housing. According to an exemplary embodiment, the shimmingmaterial is encapsulated in a biocompatible material to avoid directtissue contact and corrosion.

Other shimming components can also be provided exterior to the housingor casing of an implantable medical device. For example, FIG. 18illustrates an implantable medical device 1100 according to anotherexemplary embodiment having a shimming component 1110 coupled to anexterior surface of its housing or casing 1102. According to anexemplary embodiment, the shimming component 1110 is a polymericmaterial loaded with a shimming material that is molded directly to thehousing 1102 (e.g., where a housing of a device is made of titanium or atitanium alloy, the polymeric material may be an epoxy loaded with adiamagnetic material such as silver or a silver alloy, although theparticular constituents may differ according to other exemplaryembodiments; additionally, the polymeric material may be provided on theinterior surface of the housing). According to another exemplaryembodiment, the component 1110 is a boot that surrounds the housing 1102(e.g., the boot may be a silicon rubber (or similar material) boot thathas a shimming material incorporated therein). According to yet anotherexemplary embodiment, the component 1110 is a paralyne coating that hasincorporated therein a shimming material (again, it should be noted thatthe paralyne coating may be provided on the interior surface of thehousing). It should be noted that while FIG. 18 illustrates component1110 as completely surrounding the housing 1102, according to otherexemplary embodiments, the component 1110 may only partially surroundthe housing 1102 (e.g., the component may be provided at only selectlocations on the exterior surface of the housing 1102).

As an alternative to or in addition to shimming all or a portion of themedical device housing or casing, it may also be possible to provideshimming materials on structures or elements included within the medicaldevice housing. For example, because the battery 10 is provided withinthe device enclosure 140, and is therefore not in direct contact withthe human body in which the device 100 is implanted, it may be desirableto plate or coat the exterior surface of the battery 10 with a shimmingmaterial (e.g., a diamagnetic material). According to an exemplaryembodiment, at least a portion of an interior or exterior surface of atitanium or titanium alloy battery housing 20 is coated (e.g., clad,plated, etc.) with silver or a silver alloy to a thickness sufficient toreduce image distortion caused by the housing 20 (e.g., betweenapproximately 0.0001 and 0.01 inches). According to another exemplaryembodiment in which a battery housing 20 is made of copper or a copperalloy, the housing 20 may be coated (e.g., clad, plated, etc.) withtitanium or titanium alloy to a thickness sufficient to reduce imagedistortion caused by the housing 20 (e.g., between approximately 0.0001and 0.01 inches). It should be noted that all or a portion of theinterior and/or exterior surface of the battery housing may be plated orcoated with a shimming material, and that the coating and platingmethods described herein with respect to FIGS. 8-18 may be utilized asmay be appropriate in a particular battery configuration (e.g., two ormore portions of the housing may be plated with different amounts ofshimming material, as shown for example in FIG. 12 in the context of animplantable medical device).

According to another exemplary embodiment, a non-functional shimmingcomponent (e.g., a shimming member or element) may be added to a hybridor circuit board (e.g., hybrid 200) to shim the hybrid. For example, asshown in FIG. 7, a shimming component 210 (e.g., member, element, etc.)is added directly to the hybrid in order to shim the hybrid. Thecomponent 210 serves no electronic purpose for the hybrid, and in effectis a “dummy” component (e.g., a block of shimming material) provided forthe purpose of shimming the hybrid 200. The component 210 may beprovided in any suitable location on the hybrid (e.g., adjacent toanother component that would benefit from being shimmed, in a blank areaon the hybrid, etc.). The size, shape, and/or configuration of thecomponent 210 may vary according to other exemplary embodiments. Itshould also be noted that more than one such component may be providedon the hybrid. One advantageous feature of providing shimming componentsdirectly on the hybrid is that the size of the device need not beincreased to accommodate the shimming component (since the hybrid has afixed size, and the shimming components fit in otherwise unused space onone or both sides of the hybrid).

According to another exemplary embodiment, an implantable medical deviceincludes a header block that includes a number of metallic componentsfor use by the device. FIG. 19 is a schematic plan view of a device 1200that includes a header block 1210. Shimming components 1220 and 1230 maybe provided within the header block to shim other metallic componentsprovided in the header block and/or to shim the device as a whole. Oneadvantageous feature of providing shimming components within the headerblock is that the shimming components are provided in relatively closeproximity to the metallic components in the header block.

The type of MRI scan can also be designed to reduce distortion.Different types of scans can have different effects on the imagedistortion. For example, a gradient echo pulse sequence isdisadvantageous for mitigating image distortion and a spin echo sequenceis superior. Further, a technique called shimming can also be used toaddress image distortion. Image distortion is better on lower staticmagnetic field strength machines and is worse on higher static magneticfield strength machines. Ways to minimize the image distortion throughthe scan type, image processing, and shimming will be described indetail below.

According to an exemplary embodiment, the MRI machine and associatedimage processing system are used to address the image distortionresulting from an implant, such as a cranial implant. The adjustmentsmay further reduce the distortion resulting from such a device afterapplying one or more of the other features of the invention discussedabove. In particular, the pulse sequence selection, certain imageprocessing techniques, and shimming may all be used to address orcounteract distortions resulting from the implant.

Image artifacts from metallic implants are highly dependent on thechoice of pulse sequence. The particular MRI pulse sequence may beselected to reduce image distortion. There are several commonly usedpulse sequences in diagnostic MRI imaging. These include gradient echo,spin echo, and fast spin echo pulse sequences, among others. Spin-echopulse sequences are inherently less susceptible to magnetic fielddistortion artifacts relative to gradient echo sequences. Therefore, aspin echo sequence may be selected to reduce image distortion associatedwith the implant.

Image processing techniques may also be utilized to address imagedistortion associated with an implanted cranial device. For example,image processing software may be used to correct for known distortions.In addition to a general application of image processing techniques tocorrect for distortion, in a preferred embodiment, techniques areutilized that are applicable to a specific implanted device. Suchtechniques may include using known factors, such as materialcomposition, size, and implanted location, in a processing algorithm tocompensate for distortion associated with a specific implanted device.In practice, the necessary image processing algorithm may be determinedexperimentally by acquiring images of a specific device implanted in aphantom to provide the necessary correction data.

Yet another imaging approach that may be utilized to address cranialimage distortion is the use of a wider bandwidth for the imaginggradients.

Shimming techniques may also be utilized to address magnetic fieldinhomogeneity due to an implant, such as device 100. Ideally, themagnetic field gradients associated with the presence of an implanteddevice may be addressed through the use of shim coils to correct thefield inhomogeneity. Shim coils are designed and placed on an MRI or anNMR machine to actively compensate for magnetic field inhomogeneities,doing so by providing “canceling” magnetic fields when current is runthrough the shim coils. Adjusting the currents in such shim coils tocancel the unwanted gradients is known as “active shimming.” Variousactive shimming approaches are known and used, especially in NMRspectroscopy. However, there is a need for the ability to correct formagnetic field inhomogeneities in MRI, and certain NMR shimmingprinciples and devices may be applied in accordance with the presentinvention.

Certain conventional MRI machines utilize shim coils to correct for themagnetic field inhomogeneity due to placement of the patient in thefield. The shim coils are intended to address first order gradients dueto the patient, i.e., to correct for the linear variation in magneticfield strength with position due to the presence of the patient in thefield. Such shim coils may be useful to adjust the field inhomogeneitiesdue to an implant using approaches in accordance with certainembodiments of the present invention. However, implants, especiallythose including ferromagnetic materials, may result in higher ordergradients, e.g., second order gradients having quadratic variations infield strength. The active shim coils presently in use on MRI machinesto correct first order gradients may not suitably address the secondorder gradients associated with an implant. Accordingly, in anembodiment of the present invention, additional shim coils are installedand utilized to correct for the presence of the implant. Likewise,additional shim coils may be utilized to correct higher order gradients,depending on the desired level of correction.

Active shimming may be performed manually by changing the currentsupplied to various shim coils to achieve the best gradient correction.However, computers have been used to automate such shimming with varyingdegrees of success because the process of shimming tends to be complexand tedious, especially due to the interactions between multiple shimcoils when correcting second and higher order gradients.

According to an exemplary embodiment, a custom shim for the implant isutilized. The custom shim may be created because the device propertiesare known and therefore may be specifically addressed by an activeshimming technique. In a preferred embodiment, custom software may beutilized to automate the active shimming, and may be customized for aspecific cranial device, and/or a specific MRI machine.

According to an exemplary embodiment, the distortion associated with theimplant is mitigated as follows. A patient having an implant ispositioned in an MRI machine for image acquisition. Prior to imaging,shim coils are used to adjust the magnetic field to address unwantedgradients in the field caused by the implant (and patient). Theadjustment may include the use of shim coils to address first ordergradients or may involve adjusting the current in multiple shim coils toaddress first order, second order, and even higher order gradients. Oncethe field inhomogeneities have been addressed via active shimming(either manually, or automatically, utilizing custom shimming softwareor other automating techniques), the image may be acquired, preferablyby utilizing a spin echo pulse sequence. Once the data has beenacquired, the image may be reconstructed using conventionalreconstruction techniques that are modified to adjust for knowndistortions associated with the implant, such as the use of a customimage processing routine to adjust for the specific implanted device.

While the implantable medical device is described herein in the contextof an implantable neurological stimulation device, it should beunderstood that other types of implantable medical devices may alsobenefit from the use of the features described herein, including, by wayof example, implantable defibrillators, pacemakers, cardioverters,cardiac contractility modulators, drug administering devices, diagnosticrecorders, cochlear implants, and the like.

It is important to note that the construction and arrangement of theimplantable medical devices as shown in the various exemplaryembodiments is illustrative only. Although only a few embodiments havebeen described in detail in this disclosure, those skilled in the artwho review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Forexample, elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. Accordingly, all such modificationsare intended to be included within the scope of the present invention.The order or sequence of any process or method steps may be varied orre-sequenced according to alternative embodiments. Other substitutions,modifications, changes and omissions may be made in the design,operating conditions and arrangement of the various exemplaryembodiments without departing from the scope of the present inventions.

1. A lithium battery comprising: a housing; a first electrode providedwithin the housing; a first tab coupled to the first electrode; a secondelectrode provided within the housing; a second tab coupled to thesecond electrode; a pin coupled to the second tab and extending to alocation outside the housing; and a bracket provided within the housingto couple one of the first tab and the second tab to the housing, thebracket comprising a material comprising vanadium.
 2. The lithiumbattery of claim 1, wherein the pin is formed from a material comprisingvanadium.
 3. The lithium battery of claim 1, wherein the second tab isformed from a material comprising vanadium.
 4. The lithium battery ofclaim 1, wherein the first tab is formed from a material comprisingvanadium.
 5. The lithium battery of claim 1, wherein the second tab andthe pin are formed from a material comprising vanadium.
 6. The lithiumbattery of claim 1, wherein the material comprising vanadium is avanadium alloy.
 7. The lithium battery of claim 1, wherein the secondtab is formed from a material comprising vanadium and the secondelectrode comprises copper.
 8. The lithium battery of claim 1, whereinthe housing comprises a material selected from the group consisting ofaluminum, titanium, copper, and alloys and combinations thereof.
 9. Thelithium battery of claim 1, wherein the housing comprises an aluminumfoil and polymer composite material.
 10. The lithium battery of claim 1,wherein the battery is configured for use in an implantable medicaldevice.
 11. The lithium battery of claim 1, wherein the implantablemedical device is an implantable neurological stimulation device.
 12. Alithium battery comprising: a housing; a first current collectorelectrically coupled to a positive electrode; a second current collectorelectrically coupled to a negative electrode; a terminal coupled to oneof the first current collector and the second current collector; and amember within the housing coupling the second current collector to thehousing, wherein the member comprises a material selected from the groupconsisting of vanadium and vanadium alloys.
 13. The lithium battery ofclaim 12, wherein the terminal comprises vanadium and is coupled to thesecond current collector.
 14. The lithium battery of claim 12, whereinthe second current collector comprises vanadium.
 15. The lithium batteryof claim 12, wherein the terminal and the second current collectorcomprise vanadium.
 16. The lithium battery of claim 12, wherein thefirst current collector comprises vanadium and the potential of thepositive electrode is less than approximately 3.6 volts.
 17. The lithiumbattery of claim 12, wherein the terminal comprises titanium and thesecond current collector comprises vanadium.
 18. The lithium battery ofclaim 12, further comprising a housing comprising a material selectedfrom the group consisting of aluminum, titanium, copper, and alloys andcombinations thereof.
 19. The lithium battery of claim 18, wherein thehousing comprises an aluminum foil and polymer composite material. 20.The lithium battery of claim 12, wherein the housing comprises titanium.21. An implantable medical device comprising: a housing configured forimplantation in a human body; and a lithium battery provided within thehousing, the battery comprising a member formed of a vanadium material,the member coupling the housing to a tab that extends from an electrode.22. The implantable medical device of claim 21, wherein the lithiumbattery comprises a terminal comprising a material selected from thegroup consisting of vanadium and vanadium alloys.
 23. The implantablemedical device of claim 21, wherein the tab comprises a materialselected from the group consisting of vanadium and vanadium alloys. 24.The implantable medical device of claim 23, wherein the electrode is anegative electrode.
 25. The implantable medical device of claim 23,wherein the lithium battery comprises a terminal comprising a materialselected from the group consisting of vanadium and vanadium alloys. 26.The implantable medical device of claim 21, wherein the implantablemedical device is selected from the group consisting of a defibrillator,a pacemaker, a cardioverter, a cardiac contractility modulator, a drugadministering device, a diagnostic recorder, and a cochlear implant. 27.The implantable medical device of claim 21, wherein the implantablemedical device is an implantable neurological stimulation device.